but when I exchange command to flac.exe (it's in the same folder) and remove in parameters everything left of @ and place just -6 for compression mode, nothing happens. I can, however, drag'n'drop single file to that button, and it will work, but I want to make a selection of few files and pressing button, to convert them into same folder.

%S insert the names of all selected files into the command line. Names containing spaces will be surrounded by double quotes. Please note the maximum command line length of 32767 characters.%S10 insert the names of the first 10 selected files (max.) into the command line. Allows to limit the number of file names passed to the program. You can use any other number.

FLAC does not support input lists defined via @listname. But it does accept multiple input files at once.

Thank you very much - I didn't realise it doesn't accept input files like wavpack does. Shame on me.If added --delete-input-file in fornt of parameter, it does exactly what I want.Thank you again, deus-ex.